The mouse is a commonly used input device for computer display terminals, and provides signals to control the position of a cursor on the display face. The mouse is configured as a small, box-like device and is placed on and moved over a flat surface in various directions. As position changing signals are generated by the mouse, they are transmitted to the terminal which causes a corresponding movement of the cursor. While the mouse is useful for many applications, it requires that one hand be withdrawn from the terminal's keyboard to control its movement. Recently, a new mechanism has been developed which provides directional control signals for a cursor, but allows both of the users hands to remain in contact with the keyboard. In U.S. Pat. No. 4,712,101 to C. F. Culver, this mechanism is shown as comprising a rotatable shaft on which a cylinder has been mounted. The mechanism is constructed as part of or adjacent to a keyboard and is positioned on the user side of the shift bar. In one configuration, it comprises a separate entity which sits immediately in front of the keyboard.
The cylinder rotates with the shaft as the shaft rotates; however, the cylinder is able, simultaneously, to translate longitudinally along the axis of the shaft. One encoder is coupled to the shaft and provides rotary shaft movement signals which control one direction of movement of the cursor. Another encoder is coupled to the cylinder and provides a signal indicative of its longitudinal movement. That signal is employed to control the cursor's movement in a second direction on the display. As a result of this structure, a cursor's position in the display is controlled through the action of one hand both rotating and translating the mechanism while still in contact with the keyboard.
Culver employs a variety of encoders to derive his motion signals. In one version, he employs a code wheel rotatable with the shaft and a second encoder wheel which is operated by a cable connected to the cylinder. In another version, the rotary wheel is coupled to the shaft by a gear arrangement while the longitudinal movement sensing is accomplished by a linear encoder directly coupled to the cylinder. In still another version, Culver suggests the use of a linear resistive strip for longitudinal positional sensing.
In U.S. Pat. No. 4,724,715 Culver further describes a number of design modifications to the structures shown in his '101 patent. Those modifications revolve about the use of analogue elements as position sensors rather than the digital encoders shown in his earlier patent. Despite the acknowledged benefits of Culver's input mechanism, his implementations are expensive and some are difficult to maintain in adjustment when operated by the user. Furthermore, Culver employs a number of mechanical devices to derive his position sensing outputs. To the extent that sensing and position encoding can be performed electrically, system reliability increases and product and assembly costs decrease.
Accordingly, it is an object of this invention to provide an improved cursor control mechanism.
It is another object of this invention to provide a cursor control mechanism which employs electrical sensing to determine position and movement.
It is a further object of this invention to provide an improved cursor control mechanism which is less expensive and more reliable than the prior art.